1. Field of the Invention
This invention relates to a signal processing apparatus. In addition, this invention relates to a method of signal transmission. Furthermore, this invention relates to a signal transmission medium.
2. Description of the Related Art
Japanese published unexamined patent application 10-285234 discloses a signal processing circuit which discriminates a head packet and stores it into a memory in the reception of split packets via a serial interface. The signal processing circuit stores normal data into the memory even when a packet omission takes place. Split packets are transmitted via an IEEE1394 serial bus, a physical layer circuit, and a link core. Values DBC, FN, and DBS are set in a first quadlet of a CIP header of each split packet. The signal processing circuit discriminates a head packet by using values DBC, FN, and DBS therein. In addition, the signal processing circuit decides a packet omission by using values DBC, FN, and DBS. In the case where a packet omission is decided, the signal processing circuit stores only normal packets into a FIFO memory.
Japanese published unexamined patent application 11-45512 discloses that packets inputted from an IEEE1394 serial bus are combined into a transport stream, and the transport stream is converted into a program stream before being recorded on a DVD (a digital versatile disc). During the recording of the program stream on the DVD, a pack length of the program stream and a sector length of the DVD are accorded with each other. In addition, PCR information (time information of the transport stream) is converted into SCR information (time information of the program stream). PSI/SI sections are separated from the transport stream. Attribute information of video and audio data placed in the transport stream is generated from the PSI/SI sections. The attribute information is recorded on an innermost portion of the DVD.
Japanese published unexamined patent application 10-190705 discloses a signal transmission apparatus designed for communications of data of 2,048 bytes through the use of a digital interface of the IEEE1394 standards. A 4-byte time stamp and 124-byte padding data are added to a 2048-byte pack in an MPEG program stream so that the whole byte length of addition-resultant data will be equal to a multiple of 16. The addition-resultant data are divided by a divisor (for example, 32) equal to a multiple of 2, being thereby converted into data blocks each having a byte length (for example, a 68-byte length) equal to a multiple of 4. The number of the data blocks is equal to the divisor. A header such as a CIP header is added to a given number of data blocks to form a packet.
A DVD-Audio has an audio file containing A packs (audio packs), RTI packs (real time information packs), and SPCT packs (still picture packs). Some transmitted contents information has a file structure in which an audio file and a video file are multiplexed. The video file contains V packs (video packs).
In the case where an audio data stream having such a multiplexed file structure and containing multiple-channel audio information is transmitted in conformity with the IEEE1394 standards, it is important to manage audio channels for accurate reproduction of the audio information. In a prior-art digital interface, it is difficult to easily capture channel information. Specifically, in a prior-art IEC958 system, it is difficult to perform channel management related to multiple-channel audio contents.
In the case of transmission of a data stream having a multiplexed file structure, it is desirable to implement a signal formatting process to previously notify a reception side of what decoding process is necessary. Specifically, the signal formatting process is designed to enable a digital interface to identify the type of compression by which compression-resultant data stored in the data stream are generated. Also, in this case, selective reception and efficient reproduction of the information from the data stream are desired. An example of the selective reception is as follows. When received data are of an undecodable type, a reception process is suspended. An example of the efficient reproduction is as follows. A previous decision is made as to whether or not data to be received is of a compressed type, and reproduction of information from the data is implemented in response to a result of the decision.
Generally, data of a DVD-Audio format represent high-quality audio information. In the case of transmission of high-quality audio data, it is important to consider copyright management. It is sometimes desirable to permit making a copy in a manner such that high-quality audio data are converted into low-quality audio data (for example, audio data having a quality comparable to that of a CD) before the low-quality audio data are copied.